Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Numerator
Less: distributed earnings allocated to participating securities	$ (407)	$ (497)	$ (813)	$ (995)
Net loss attributable to SLGOP common unitholders (numerator for basic earnings per unit)	(360,601)	(44,373)	(400,738)	(37,120)
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	0	1,103	0	806
Net loss attributable to SL Green common stockholders (numerator for diluted earnings per share)	$ (384,682)	$ (48,289)	$ (426,657)	$ (40,247)
Denominator
Common stock shares excluded from the diluted shares outstanding (shares)	1,529,312	528,607	1,381,565	482,130
SL Green Operating Partnership
Numerator
Net loss attributable to SLGOP common unitholders (numerator for diluted earnings per unit)	$ (383,776)	$ (46,689)	$ (425,844)	$ (38,446)
Less: distributed earnings allocated to participating securities	(906)	(497)	(813)	(995)
Net loss attributable to SLGOP common unitholders (numerator for basic earnings per unit)	(384,682)	(47,186)	(426,657)	(39,441)
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	0	(1,103)	0	(806)
Net loss attributable to SL Green common stockholders (numerator for diluted earnings per share)	$ (384,682)	$ (48,289)	$ (426,657)	$ (40,247)
Denominator
Basic weighted average common units outstanding (in shares)	68,341,000	67,900,000	68,263,000	68,099,000
Stock-based compensation plans (shares)	0	1,120,000	0	1,139,000
Contingently issuable units (in shares)	0	0	0	184,000
Diluted weighted average common units outstanding (shares)	68,341,000	69,020,000	68,263,000	69,422,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,529,312	528,607	1,381,565	482,130